1. Field of the Invention
This invention pertains to highway delineation and safety devices comprising flexible plastic structures which simulate the distant appearance of a plastic tube. More particularly, the subject matter of this invention relates to an elongated, flexible highway safety device which has the appearance of a tube but is not subject to elastic failure generally occurring in tubes as they are impacted by high-speed vehicles.
2. Prior Art
The uses of plastic tubing within the field of highway safety include its incorporation in barriers, delineators or markers. Such devices are provided to attract the attention of an observer for purposes of safety, guidance or information awareness. For example, barriers fabricated of plastic tubing may be positioned in the path of moving traffic to divert the direction of movement along a different course. Likewise, such tubing may be positioned along a roadside to delineate curvature or other changes in direction which a traveler must follow. Other applications involve use as a marker for providing day or nighttime identification of roadsides, hazardous areas and conditions where extra caution or attention may be required. In addition to the obvious characteristic of high visibility, tubular structure provides the benefit of minimal material cost because most of the material making up the tube is exposed at the tube surface. The tubular configuration also offers the desirable features of stiffness, resilience, flexibility, and light weight. For example, tubular structure has been effective against frequent impact where the stiff tubular structure is designed to deflect under a vehicle and then rebound to its original orientation.
It is well-known, however, that the same tubular structure which develops these favorable characteristics also includes a major deficiency in highway applications. Specifically, plastic tubes tend to form weakened "hinge" areas, where the elastic limit of the material is exceeded during impact. For example, FIG. 1 shows a plastic tube 10 having cylindrical shape 15 which has been deflected 13 by a bending moment M, displacing the tube from a straight orientation 16 to a bent orientation 17. Although those parts of the tube 11 and 12 away from the bend are substantially unaffected, the plastic at the localized hinge area 13 is greatly stressed. Typically, sharp dimples 18 form on each side of the bend 13 where the elasticity of the tube wall is exceeded. The result is loss of stiffness and resilience at that local hinge site. Furthermore, this weakened location becomes the likely target for recurring collapse, causing further damage to the tubular structure and reducing its ability to restore itself to upright position. After numerous repetitions, the tube becomes permanently deformed, as shown in FIG. 1, and must be replaced.
Where plastic tube structure is used in a horizontal barrier device, additional problems arise because of the limited stength of the tube when unsupported. For example, long lengths of tube frequently collapse because of their own weight if suspended at one end. Unsupported intermediate sections of tube tend to sag or even collapse to form a hinge point similar to that in FIG. 1. Here again, a first collapse in tube structure causes weakened elastic character inevitably leading to a permanent sagging structure which may destroy functionality as well as appearance.
What is needed, therefore, is a vertical tubular structure which can deform without localized elastic failure and thereby remain serviceable, despite repeated impacts. Furthermore, it would be beneficial to have a tubular structure capable of supporting its own weight whether suspended in the horizontal or vertical orientation.